Limits to future expansion of surface‐melt‐enhanced ice flow into the interior of western Greenland

Abstract

Moulins are important conduits for surface meltwater to reach the bed of the Greenland Ice Sheet. It has been proposed that in a warming climate, newly formed moulins associated with the inland migration of supraglacial lakes could introduce surface melt to new regions of the bed, introducing or enhancing sliding there. By examining surface strain rates, we found that the upper limit to where crevasses, and therefore moulins, are likely to form is ~1600 m. This is also roughly the elevation above which lakes do not drain completely. Thus, meltwater above this elevation will largely flow tens of kilometers through surface streams into existing moulins downstream. Furthermore, results from a thermal ice sheet model indicate that the ~1600 m crevassing limit is well below the wet‐frozen basal transition (~2000 m). Together, these data sets suggest that new supraglacial lakes will have a limited effect on the inland expansion of melt‐induced seasonal acceleration.

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

“…In contrast, the weight of evidence suggests a seasonal increase in drainage efficiency beneath the GrIS [62,64] with no net acceleration on annual timescales [84,87]. Furthermore if meltwater does continue to access the bed at increasingly high elevations (which may not be possible [52]), it will likely only be able to do so through the rapid drainage of large supraglacial lakes. We believe that the delivery of such large volumes of water will be capable of rapid channelisation, as is currently indicated by observations of lake drainage at lower elevations [9,55,81], and that such channelisation will similarly result in only a limited or even negative net effect on annual ice velocity [90••, 91].…”

“…Due to a combination of decreasing meltwater availability and a reduction in crevassing due to the stress regime, the potential for hydrofracture and thus the density of moulins decreases with elevation [44,51,52]. In west Greenland, Poinar et al [52] observed a moulin density of 0.02 km −2 between 1500-and 1600-m elevations which compared with 12 km −2 at lower (0-1100 m) elevations [51].…”

“…In west Greenland, Poinar et al [52] observed a moulin density of 0.02 km −2 between 1500-and 1600-m elevations which compared with 12 km −2 at lower (0-1100 m) elevations [51]. This reduction in moulin density ensures that at high elevations, meltwaters are often transported considerable distances from the source of meltwater generation to the point of input to the englacial drainage system [34].…”

Force Balance along Isunnguata Sermia, West Greenland

“…Knowledge of the thermal state of the ice-bed interface far from the ice sheet margin is lacking. However, there is broad agreement by numerical models that temperate basal conditions extend well inland of the ELA at our study area (Seroussi et al, 2013;Meierbachtol et al, 2015;Poinar et al, 2015), despite evidence of low geothermal heat flux (Meierbachtol et al, 2015). Consequently, it is unlikely that increased basal slip results from a frozen to temperate transition.…”

“…Surface crevasses provide one mechanism facilitating meltwater transport. It has been suggested that conditions promoting crevasse formation are limited to below ∼1400 m (Clason et al, 2015) to 1600 m elevation (Poinar et al, 2015) in the study area. Meltwater-induced seasonal variations in ice motion have been observed to elevations reaching ∼1500-1600 m (Bartholomew et al, 2011;Palmer et al, 2011).…”